Send Emails To Specific Users

I have a frequent need to send emails to specific users across multiple user groups, without sending the email to all users in each of those groups. As it stands, I would have to enter only one username at a time to send an email from the ACP. The Email Users does not allow for entering multiple usernames in the User Name: field, as with sending emails to multiple recipients as in t-bird for example.

I'm not sure how to even ask for a specific solution. If I could send to multiple usernames that would be great, but even if I could generate an email list from a list of specific usernames, that would be fine as well since I could then copy and paste those emails into t-bird which automatically formats them with commas.

There may already be some kind of solution in the core for this and I just haven't found it yet. I hope to get some interest on this as I do need a solution for this. Anyone else interested in participating in this please sound off, but even if I am the only one I'm willing to foot the cost on it if someone is willing to write an add on.